How this calculator works
The liner has to go down one side of the pond, across the bottom and up the other side, with some left over on the bank. So the liner length is the pond length plus twice the depth plus the overlap, and the width works the same way. The overlap is the liner that lies on the ground around the edge, held down by rocks or coping: a foot at each edge is usual. Round up to a whole foot, and then to the next roll size in stock.
Worked example: a pond 10 ft long, 8 ft wide and 2 ft deep, with a 1 ft overlap on each edge, needs a liner 16 ft long and 14 ft wide, an area of 224 ft². The next common roll size is 15 × 20 ft. With a 1 ft depth it would be 14 × 12 ft, and with a 2 ft overlap 18 × 16 ft. A small 6 × 4 ft pond 1½ ft deep needs 11 × 9 ft, and a 20 × 15 ft pond 3 ft deep 28 × 23 ft (25 × 30 ft).
Liner size for common pond sizes (1 ft overlap on each edge)
The liner length and width, and the next common roll size.
| Pond | Depth | Liner | Next common size |
|---|---|---|---|
| 6 × 4 ft | 1.5 ft | 11 × 9 ft | 10 × 12 ft |
| 8 × 6 ft | 2 ft | 14 × 12 ft | 12 × 15 ft |
| 10 × 8 ft | 2 ft | 16 × 14 ft | 15 × 20 ft |
| 12 × 8 ft | 2 ft | 18 × 14 ft | 15 × 20 ft |
| 12 × 10 ft | 2.5 ft | 19 × 17 ft | 20 × 20 ft |
| 15 × 10 ft | 2.5 ft | 22 × 17 ft | 20 × 25 ft |
| 20 × 15 ft | 3 ft | 28 × 23 ft | 25 × 30 ft |
Tips before you buy
- Use the longest, widest and deepest points of the pond, even if the shape is irregular.
- Add a foot of length and width for every shelf or step, since the liner follows each level.
- Put underlayment (or old carpet or sand) under the liner to protect it from roots and stones.
- Leave the liner to warm in the sun before you lay it, so that it is flexible and settles into the folds.
- Fill the pond slowly and smooth the folds as it fills, then trim the excess only after the pond is full and has settled.
Tools & materials for this project
Affiliate links As an Amazon Associate we earn from qualifying purchases. These links do not change what you pay.
Frequently asked questions
How do I work out what size pond liner I need?
Add the length, twice the depth and the overlap, and do the same for the width. For a 10 × 8 ft pond 2 ft deep with a 1 ft overlap that gives 16 × 14 ft.
How much overlap should a pond liner have?
A foot at each edge is usual (so 2 ft added to the length and width), more if you want to hide the edge under rocks or coping. A foot more is needed for each shelf or step.
What size liner for a 10 × 8 pond?
A liner 16 × 14 ft if the pond is 2 ft deep, so the next common roll size is 15 × 20 ft.
Do I need underlayment under a pond liner?
It is a good idea: it protects the liner from roots, stones and sharp edges. Buy about the same area as the liner (224 ft² here).
What happens if my pond is deeper?
The liner grows by 2 ft in each direction for every extra foot of depth. At 3 ft deep the same pond needs 18 × 16 ft.
Add this calculator to your website
Running a blog, a contractor site or a class page? You can put this calculator on it for free. Copy the code below, and please leave the link underneath the calculator in place. The small script just resizes the frame to fit the results; if your site strips scripts, the calculator still works inside a scrolling frame.
Related calculators & guides
Estimates only. Results assume standard materials and simple shapes. Supplier products vary, and the final call on quantity, structure and safety is yours. Check your local code and your supplier's guidance before ordering.